In recent years, portable terminal devices such as smart phones with a digitizer feature have been commercialized and become popular in the market. A digitizer using an electronic pen enables a user to draw a line of about 0.7 mm thick and thus is more precise than a capacitive type touch panel recognizing a line of 3-4 mm thick, to thereby perform a fine work easily.
In addition, it is possible to take handwritten notes, to draw a picture, and edit an image or photo, by using an electronic pen such as a stylus. Furthermore, pressure of a force applied to the electronic pen is detected when a user holds the electronic pen in hand to write a letter and thus thickness of the letter varies depending on the detected force, to thereby enable a work with a high resolution.
To implement such a digitizer feature, a digitizer panel is provided at a lower side of a touch screen/display panel. In addition, since the digitizer panel is formed of a thin metal film, a feeble electromagnetic field is created when the digitizer panel conducts electricity, and since a built-in ultra-small metal coil is provided at the end of the portable electronic pen, an alternating magnetic field is generated in use.
Thus, when the tip of the electronic pen is close to the touch screen, the electromagnetic induction phenomenon occurs, while deformation of the electromagnetic field that has already been formed occurs on the digitizer panel disposed below the touch screen/display panel. Here, deformation of the electromagnetic field is detected through a sensor arranged at a side edge of the digitizer panel to thereby be interpreted as the actual movement of the electronic pen.
This digitizer feature is being applied to a large screen tablet personal computer (PC) employing a large display as well as a small portable terminal device such as a smart phone.
In order to use a digitizer feature using an electromagnetic induction phenomenon in a portable terminal device, a magnetic field shield sheet for shielding an electromagnetic field generated from various components of a main body of the portable terminal device, is inserted and used between the digitizer panel and a main circuit board. The main body of the portable terminal device has a variety of communication chips and antennas and generates an electromagnetic field for wireless communications.
Recently, a spread of a long-term evolution (LTE) implementing a fourth generation mobile communication technology uses radio waves much stronger than a conventional wireless communication terminal using of the 3G mobile communication system. Accordingly, an influence upon a digitizer from the strong electromagnetic field is precluded, and a reliable magnetic field shield is required for smooth magnetic field communications between the stylus and the digitizer.
Meanwhile, the portable terminal device includes a geomagnetic sensor in order to implement functions such as navigation or augmented reality by using GPS (Global Positioning System) technologies. In addition, in the case of smart phones employing the Android operating system (OS), it is an essential condition to adopt the geomagnetic sensor.
Since the magnetic field shield sheet is formed of a size corresponding to a digitizer, i.e., a display so as not to influence upon a digitizer function, it is difficult to design a gap between the magnetic field shield sheet and the geomagnetic sensor in the inside of the portable terminal device to become 2 mm or longer.
However, in the case that the magnetic field shield sheet is used in the portable terminal device in the proximity of and together with the geomagnetic sensor, the magnetic field shield sheet affects the geomagnetic sensor thereby causing the malfunction in the geomagnetic sensor.
In other words, the geomagnetic sensor can cause azimuth distortion, sensor sensitivity distortion, and magnetic hysteresis distortion by the magnetic field shield sheet.
The azimuth distortion means a phenomenon of distorting direction of the magnetic north due to the magnetic field shield sheet, the sensor sensitivity distortion means a phenomenon of distorting sensitivity among X-, Y-, Z-axis sensors constituting the geomagnetic sensor, since the strength of the magnetic field is also changing due to the magnetic field shield sheet, and the magnetic hysteresis distortion means a phenomenon of making an error in the azimuth depending on the direction of rotation of the sensor because of the magnetic hysteresis of a magnetic substance.
Accordingly, in order to prevent the distortion of the geomagnetic sensor and in order to measure accurate azimuth, it is necessary to correct the geomagnetic sensor. However, it is possible to correct the azimuth distortion and the sensor sensitivity distortion accurately, but it is difficult to correct the magnetic hysteresis distortion accurately, to thereby weight an error of the geomagnetic sensor.
It is general to use a magnetic substance such as heatless treatment Fe-based and Co-based amorphous ribbons, ferrite sheets, or polymer sheets containing magnetic powder, as the magnetic field shield sheet. A magnetic field focusing effect to improve performance of a magnetic field shielding function and a digitizer feature, may be good in the order of high magnetic permeability Fe-based and Co-based amorphous ribbons, ferrite sheets, and polymer sheets containing magnetic powder.
The heatless treatment Fe-based and Co-based amorphous ribbons are metal sheets in themselves, and thus, have no burden to the thickness. However, the heatless treatment Fe-based and Co-based amorphous ribbons have too large magnetic permeability, and thus affect the geomagnetic sensor. As a result, the heatless treatment Fe-based and Co-based amorphous ribbons are not used ad the magnetic field shield sheets. In addition, the ferrite sheets also have too large magnetic permeability and thus affect the geomagnetic sensor. In addition, the ferrite sheets also have drawbacks of getting thick.
Thus, the conventional magnetic field shield sheet employs a polymer sheet containing magnetic powder of a relatively poor magnetic permeability. However, when compared with the Fe-based and Co-based amorphous ribbons, the polymer sheet has low magnetic permeability, to thereby cause a problem that an electronic pen such as a stylus is very expensive and sensitivity of the stylus is degraded to the half (½).
In addition, since the polymer sheet has low magnetic permeability, when compared with the Fe-based and Co-based amorphous ribbons, the polymer sheet gets thick in comparison with the Fe-based and Co-based amorphous ribbons that are thin plates of several tens of micrometers (μm) in order to improve the performance of the low magnetic permeability. Accordingly, it is difficult to cope with the trend that the terminals get thin, and the material cost is further increased due to an increase of the thickness.
Meanwhile, the magnetic hysteresis phenomenon means that a magnetic body has a hysteresis that magnetic induction values in the inside of the magnetic body do not match each other when a magnetic field is applied to the magnetic body through a rise and fall of the magnetic field, and may occur in the case that the magnetic field is applied to the magnetic body until to the magnetic body is saturated. In the case that the magnetic field does not reaches a saturation region, the magnetic induction values are repeatedly increased and decreased without causing any hysteresis along an initial magnetization curve.
In the case of the heatless treatment Fe-based amorphous ribbon among the amorphous ribbons, a value of a saturation field (Hs) that is the minimum magnetic field to obtain the saturation induction is about 0.4 G that is lower than the earth magnetic field having a value of about 0.5 G, in a magnetic hysteresis loop.
Therefore, the Fe-based amorphous ribbon sheet exhibits the magnetic hysteresis phenomenon even in the case of the change in the earth magnetic field, with the result that a geomagnetic sensor used in a terminal to which a Fe-based amorphous ribbon sheet is applied, has a fatal disadvantage that even the magnetic hysteresis phenomenon due to the Fe-based amorphous ribbon sheet should be corrected.
In addition, in the case that Fe-based and Co-based amorphous ribbon sheets are used, the geomagnetic sensor causes an azimuth hysteresis phenomenon that is generated according to the rotational direction of the geomagnetic sensor in the X-axis, Y-axis, and Z-axis sensed values when the geomagnetic sensor is rotated in the clockwise direction and the counterclockwise direction, and an azimuth hysteresis phenomenon is not accurately calibrated thereby weighting errors to the sensor operation.
Meanwhile, Korea Patent Laid-open Publication No. 10-2011-92833 proposed an electromagnetic wave absorbing sheet containing a Fe-based nanocrystalline soft magnetic powder and a carbon-based conductive material powder. The Fe-based nanocrystalline soft magnetic powder is formed of a Fe—Si—B—Nb—Cu-based alloy as an amorphous alloy. The Fe—Si—B—Nb—Cu-based alloy is preliminarily heat treated at a temperature of 350° C. to 500° C. for 45-90 minutes, to thus obtain alloy powders, the alloy powders are primarily and secondarily crushed, and then the crushed powders are meshed to be 270 mesh in particle size, to thereby obtain Fe-based nanocrystalline soft magnetic powders having nano-sized crystal grains.
The electromagnetic wave absorbing sheet is made to have a thickness of 0.5 mm, to thus absorb 10 MHz to 10 GHz band electromagnetic waves.
However, the electromagnetic wave absorbing sheet is simply used to absorb the high frequency band electromagnetic waves, and employs a kind of the polymer sheet that is made to have a thickness of 0.5 mm by mixing a Fe-based nanocrystalline soft magnetic powder having nano-sized crystal grains, with a binder. As a result, the electromagnetic wave absorbing sheet gets thick when compared with the case of using the amorphous ribbon sheet (whose thickness is about 0.06 mm or less), and also has the low magnetic permeability due to the mixture of the binder.
Korea Patent Laid-open Publication No. 10-2005-37015 discloses a metal and polymer composite having a low frequency magnetic field shielding function, wherein at least one selected from Permalloy®, Sendust®, and a rapidly solidified alloy that are metal alloys having a high magnetic permeability is included by 10 to 80 wt % in a powdered, flaky or fibrous form; a soft polymer material is included by 15 to 65 wt % as a matrix where the metal alloys are dispersed; and various additives are included by 5 to 25 wt % in order to be used to mix the metal alloys and the soft polymer material.
Further, the Permalloy® is magnetically heat treated under the magnetic field of 300 to 600 gauss and at a temperature of 600 to 1100° C. for 1-2 hours, the Sendust® is magnetically heat treated under the magnetic field of 100 to 600 gauss and at a temperature of 500 to 1100° C. for 1-2 hours, and the rapidly solidified alloy is magnetically heat treated under the magnetic field of 100 to 600 gauss and at a temperature of 300 to 500° C., for 1-2 hours. ° C.
The metal and polymer composite includes a metal alloy and a polymer material in a powdered, flaky or fibrous form, and thus has the same problem as the polymer sheet.
The aforementioned prior art discloses an electromagnetic wave absorbing sheet or a magnetic field shield sheet. However, when both an electronic pen function (i.e., a stylus function) and a navigation function are implemented in a portable terminal device such as a smart phone, the above-described conventional magnetic field shield sheet does not propose a possible solution to the problems that a distortion problem for the geomagnetic sensor is present, the thickness of the magnetic field shield sheet gets thick, and the material cost for the magnetic field shield sheet is very expensive.
Taking into account that the distortion of the azimuth and the sensor sensitivity distortion among the distortions that occur in the geomagnetic sensor due to the shield sheet can be accurately corrected, but the directional hysteresis due to the magnetic hysteresis phenomenon cannot be accurately corrected, the inventor(s) has tried to develop shield sheets that do not cause the distortion problem due to the magnetic hysteresis phenomenon, and seen that there may be little change in the magnetic permeability even though the thin-film ribbon is flaked in the case of the nanocrystalline ribbon and there is no distortion problem due to the magnetic hysteresis phenomenon because of no magnetic saturation, which leads the inventor(s) to the present invention.
In the case of using a digitizer function in the smart phone such as the conventional tablet PC or the tablet phone, the digitizer function is not activated until a sufficient force is applied onto tempered glass provided on a touch screen panel or a display panel with the tip of the electronic pen so as to feel pressure of the tip of the electronic pen. In addition, thickness of the character may be changed by detecting the intensity of the pressure of the tip of the electronic pen. Therefore, it is required to implement a contactless pen function for ease of use, improvement of durability, and improvement of sensitivity of the digitizer function.